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Subject[PATCH 20/26] x86/tdx: Add helper to convert memory between shared and private
Date
Intel TDX protects guest memory from VMM access. Any memory that is
required for communication with the VMM must be explicitly shared.

It is a two-step process: the guest sets the shared bit in the page
table entry and notifies VMM about the change. The notification happens
using MapGPA hypercall.

Conversion back to private memory requires clearing the shared bit,
notifying VMM with MapGPA hypercall following with accepting the memory
with AcceptPage hypercall.

Provide a helper to do conversion between shared and private memory.
It is going to be used by the following patch.

Co-developed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
arch/x86/include/asm/tdx.h | 18 +++++++++
arch/x86/kernel/tdx.c | 79 ++++++++++++++++++++++++++++++++++++++
2 files changed, 97 insertions(+)

diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index 286adda40fb7..20114af47db9 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -55,6 +55,15 @@ struct ve_info {
u32 instr_info;
};

+/*
+ * Page mapping types. This is software construct not part of any hardware
+ * or VMM ABI.
+ */
+enum tdx_map_type {
+ TDX_MAP_PRIVATE,
+ TDX_MAP_SHARED,
+};
+
#ifdef CONFIG_INTEL_TDX_GUEST

void __init tdx_early_init(void);
@@ -78,6 +87,9 @@ bool tdx_early_handle_ve(struct pt_regs *regs);

phys_addr_t tdx_shared_mask(void);

+int tdx_hcall_request_gpa_type(phys_addr_t start, phys_addr_t end,
+ enum tdx_map_type map_type);
+
#else

static inline void tdx_early_init(void) { };
@@ -87,6 +99,12 @@ static inline void tdx_guest_idle(void) { };
static inline bool tdx_early_handle_ve(struct pt_regs *regs) { return false; }
static inline phys_addr_t tdx_shared_mask(void) { return 0; }

+static inline int tdx_hcall_request_gpa_type(phys_addr_t start, phys_addr_t end,
+ enum tdx_map_type map_type)
+{
+ return -ENODEV;
+}
+
#endif /* CONFIG_INTEL_TDX_GUEST */

#endif /* _ASM_X86_TDX_H */
diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
index d4aae2f139a8..9ef3cf0879d3 100644
--- a/arch/x86/kernel/tdx.c
+++ b/arch/x86/kernel/tdx.c
@@ -13,6 +13,10 @@
/* TDX Module Call Leaf IDs */
#define TDX_GET_INFO 1
#define TDX_GET_VEINFO 3
+#define TDX_ACCEPT_PAGE 6
+
+/* TDX hypercall Leaf IDs */
+#define TDVMCALL_MAP_GPA 0x10001

/* See Exit Qualification for I/O Instructions in VMX documentation */
#define VE_IS_IO_IN(exit_qual) (((exit_qual) & 8) ? 1 : 0)
@@ -83,6 +87,81 @@ static void tdx_get_info(void)
td_info.attributes = out.rdx;
}

+static bool tdx_accept_page(phys_addr_t gpa, enum pg_level pg_level)
+{
+ /*
+ * Pass the page physical address to the TDX module to accept the
+ * pending, private page.
+ *
+ * Bits 2:0 if GPA encodes page size: 0 - 4K, 1 - 2M, 2 - 1G.
+ */
+ switch (pg_level) {
+ case PG_LEVEL_4K:
+ break;
+ case PG_LEVEL_2M:
+ gpa |= 1;
+ break;
+ case PG_LEVEL_1G:
+ gpa |= 2;
+ break;
+ default:
+ return true;
+ }
+
+ return __tdx_module_call(TDX_ACCEPT_PAGE, gpa, 0, 0, 0, NULL);
+}
+
+/*
+ * Inform the VMM of the guest's intent for this physical page: shared with
+ * the VMM or private to the guest. The VMM is expected to change its mapping
+ * of the page in response.
+ */
+int tdx_hcall_request_gpa_type(phys_addr_t start, phys_addr_t end,
+ enum tdx_map_type map_type)
+{
+ u64 ret;
+
+ if (end <= start)
+ return -EINVAL;
+
+ if (map_type == TDX_MAP_SHARED) {
+ start |= tdx_shared_mask();
+ end |= tdx_shared_mask();
+ }
+
+ /*
+ * Notify the VMM about page mapping conversion. More info about ABI
+ * can be found in TDX Guest-Host-Communication Interface (GHCI),
+ * sec "TDG.VP.VMCALL<MapGPA>"
+ */
+ ret = _tdx_hypercall(TDVMCALL_MAP_GPA, start, end - start, 0, 0, NULL);
+
+ if (ret)
+ ret = -EIO;
+
+ if (ret || map_type == TDX_MAP_SHARED)
+ return ret;
+
+ /*
+ * For shared->private conversion, accept the page using
+ * TDX_ACCEPT_PAGE TDX module call.
+ */
+ while (start < end) {
+ /* Try 2M page accept first if possible */
+ if (!(start & ~PMD_MASK) && end - start >= PMD_SIZE &&
+ !tdx_accept_page(start, PG_LEVEL_2M)) {
+ start += PMD_SIZE;
+ continue;
+ }
+
+ if (tdx_accept_page(start, PG_LEVEL_4K))
+ return -EIO;
+ start += PAGE_SIZE;
+ }
+
+ return 0;
+}
+
static __cpuidle u64 _tdx_halt(const bool irq_disabled, const bool do_sti)
{
/*
--
2.32.0
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